Ink jet recording is carried out in such a manner that minute ink droplets are ejected, employing various working principles and are deposited onto a recording sheet to achieve recording of images and text. The aforesaid ink jet recording exhibits advantages such as relatively high speed, low noise, and easy application to multicolor formation.
Particularly, recently, printers have been improved to produce high image quality approaching conventional photographic quality. As a result, recording sheets are also required to mimic photographic quality as well as to result in reproduction of the feel (such as glossiness, smoothness, and stiffness) of conventional silver salt photography. However, problems still remain with regard to lightfastness, waterfastness and moisture resistance.
In order to overcome problems due to the use of the aforesaid water-soluble dye ink, a method has been known in which, for improvement of waterfastness or lightfastness, resinous micro-particles (being a latex) are incorporated into water-soluble dye ink so that the printed portions are covered (for example, refer to Patent Documents 1–4).
On the other hand, as one of the methods for reproducing the feel of silver salt photography, known is a method which employs a so-called swelling type recording sheet which is prepared by applying hydrophilic binders such as gelatin or polyvinyl alcohol onto a support. However, the aforesaid method causes problems in which the rate of ink absorption is low, the surface tends to be sticky after printing, and images tend to bleed while affected by humidity during storage. Specifically, due to the low rate of ink absorption, ink droplets mix with each other to tend to result in bleeding between different colors as well as beading between the same color due to mixing of ink droplets prior to absorption, whereby it is extremely difficult to achieve the desired silver salt photographic quality.
In order to overcome the aforesaid problems, so-called void type recording sheets have played a main role while replacing the aforesaid swelling type recording sheets. Void type recording sheets are characterized in their high rate of ink absorption due to the absorption of ink into micro-voids. However, when the void type ink jet recording media (hereinafter also referred to simply as recording media) capable of achieving higher image quality and a water-soluble dye ink are combined, image fading, due to gases in the storage ambience, has been realized as a great problem. Image fading mechanism due to the aforesaid gases is not yet completely understood. However, it is assumed to be as follows. Gases in a storage ambience, especially oxidizing gases easily reach, via the void structure, dyes which have penetrated into a void type ink jet recording medium and decompose dye molecules, resulting image fading.
In order to minimize fading due to such oxidizing gases, it is possible to use a method in which after printing images on a recording medium, the resulting surface is subjected to a lamination treatment, or an image printed recording medium is stored in a frame capable of shielding from such gases. However, each of these methods necessitates post-treatment. As a result, processing becomes more complex and induces an increase in cost due to additional preparation of apparatuses for that.
In order to overcome such drawbacks, it is proposed that by printing on a recording medium employing a water-soluble dye ink comprised of resinous micro-particles, such particles remain on the surface of the aforesaid recording medium and subsequently is subjected to film formation which serves as a gas barrier, whereby the penetration of oxidizing gases into the aforesaid recording medium is minimized (refer, for example, to Patent Document 5). Film formation, as described herein, refers to a process in such a manner that the void structure portion of the uppermost surface of the recording media is filled with resinous micro-particles and immediately, the resulting resinous micro-particles are fuse with each other. Further, by achieving the film formation on the uppermost layer, surface roughness of the recording medium varies between prior to and after the deposition of ink droplets, resulting in more smoothness after printing.
In the aforesaid method, specifically when silica micro-particles are employed as inorganic micro-particles which form the void structure, the aforesaid silica particles exist together with cationic binders in the form of micro-particles and contribute to achieve compatibility between bleeding resistance and high glossiness. However, in the aforesaid constitution, electric properties of micro-particles incorporated into ink largely affect the layer properties. Namely, when ink comprised of anionic micro-particles is printed on the highly cationic surface of the recording medium, anionic micro-particles tend to aggregate on the surface of the recording medium, whereby glossiness is degraded due to formation of a roughness structure.
The above-described aggregation may affect ink absorption property resulting in deterioration of ink absorption.
Further, when image recording is achieved employing a water-soluble dye ink, problems occur during storage in which bleeding tends to occur. As a result, urgently sought is a means to improve storage stability of images prepared employing dye inks.
(Patent Document 1)
Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 55-18412 (claims)
(Patent Document 2)
JP-A No. 3-6270 (claims)
(Patent Document 3)
JP-A No. 3-160068 (claims)
(Patent Document 4)
JP-A No. 3-163175 (claims)
(Patent Document 5)
JP-A No. 2001-187852 (claims)